Merge pull request #3343 from camilamacedo86/cherry-pick-project-file

📖 apply changes done in the pr 3287

Author: k8s-ci-robot

docs/book/src/reference/project-config.md

@@ -2,7 +2,74 @@
 
 ## Overview
 
-The Project Config represents the configuration of a Kubebuilder project. All projects that are scaffolded with the CLI will generate the `PROJECT` file in the projects' root directory.
+The Project Config represents the configuration of a KubeBuilder project. All projects that are scaffolded with the CLI (KB version 3.0 and higher) will generate the `PROJECT` file in the projects' root directory. Therefore, it will store all plugins and input data used to generate the project and APIs to better enable plugins to make useful decisions when scaffolding.
+
+## Example
+
+Following is an example of a PROJECT config file which is the result of a project generated with two APIs using the [Deploy Image Plugin][deploy-image-plugin].
+
+```yaml
+# Code generated by tool. DO NOT EDIT.
+# This file is used to track the info used to scaffold your project
+# and allow the plugins properly work.
+# More info: https://book.kubebuilder.io/reference/project-config.html
+domain: testproject.org
+layout:
+  - go.kubebuilder.io/v4
+plugins:
+  deploy-image.go.kubebuilder.io/v1-alpha:
+    resources:
+      - domain: testproject.org
+        group: example.com
+        kind: Memcached
+        options:
+          containerCommand: memcached,-m=64,-o,modern,-v
+          containerPort: "11211"
+          image: memcached:1.4.36-alpine
+          runAsUser: "1001"
+        version: v1alpha1
+      - domain: testproject.org
+        group: example.com
+        kind: Busybox
+        options:
+          image: busybox:1.28
+        version: v1alpha1
+projectName: project-v4-with-deploy-image
+repo: sigs.k8s.io/kubebuilder/testdata/project-v4-with-deploy-image
+resources:
+  - api:
+      crdVersion: v1
+      namespaced: true
+    controller: true
+    domain: testproject.org
+    group: example.com
+    kind: Memcached
+    path: sigs.k8s.io/kubebuilder/testdata/project-v4-with-deploy-image/api/v1alpha1
+    version: v1alpha1
+    webhooks:
+      validation: true
+      webhookVersion: v1
+  - api:
+      crdVersion: v1
+      namespaced: true
+    controller: true
+    domain: testproject.org
+    group: example.com
+    kind: Busybox
+    path: sigs.k8s.io/kubebuilder/testdata/project-v4-with-deploy-image/api/v1alpha1
+    version: v1alpha1
+version: "3"
+```
+## Why do we need to store the plugins and data used?
+
+Following some examples of motivations to track the input used:
+- check if a plugin can or cannot be scaffolded on top of an existing plugin (i.e.) plugin compatibility while chaining multiple of them together.
+- what operations can or cannot be done such as verify if the layout allow API(s) for different groups to be scaffolded for the current configuration or not.
+- verify what data can or not be used in the CLI operations such as to ensure that WebHooks can only be created for pre-existent API(s)
+
+Note that KubeBuilder is not only a CLI tool but can also be used as a library to allow users to create their plugins/tools, provide helpers and customizations on top of their existing projects - an example of which is [Operator-SDK][operator-sdk]. SDK leverages KubeBuilder to create plugins to allow users to work with other languages and provide helpers for their users to integrate their projects with, for example, the [Operator Framework solutions/OLM][olm]. You can check the [plugin's documentation][plugins-doc] to know more about creating custom plugins.
+
+Additionally, another motivation for the PROJECT file is to help us to create a feature that allows users to easily upgrade their projects by providing helpers that automatically re-scaffold the project. By having all the required metadata regarding the APIs, their configurations and versions in the PROJECT file. For example, it can be used to automate the process of re-scaffolding while migrating between plugin versions. ([More info][doc-design-helper]).
 
 ## Versioning
 
@@ -15,30 +82,30 @@ The `PROJECT` version `3` layout looks like:
 ```yaml
 domain: testproject.org
 layout:
-- go.kubebuilder.io/v3
+  - go.kubebuilder.io/v3
 plugins:
   declarative.go.kubebuilder.io/v1:
     resources:
-    - domain: testproject.org
-      group: crew
-      kind: FirstMate
-      version: v1
+      - domain: testproject.org
+        group: crew
+        kind: FirstMate
+        version: v1
 projectName: example
 repo: sigs.k8s.io/kubebuilder/example
 resources:
-- api:
-    crdVersion: v1
-    namespaced: true
-  controller: true
-  domain: testproject.org
-  group: crew
-  kind: Captain
-  path: sigs.k8s.io/kubebuilder/example/api/v1
-  version: v1
-  webhooks:
-    defaulting: true
-    validation: true
-    webhookVersion: v1
+  - api:
+      crdVersion: v1
+      namespaced: true
+    controller: true
+    domain: testproject.org
+    group: crew
+    kind: Captain
+    path: sigs.k8s.io/kubebuilder/example/api/v1
+    version: v1
+    webhooks:
+      defaulting: true
+      validation: true
+      webhookVersion: v1
 ```
 
 Now let's check its layout fields definition:
@@ -68,4 +135,9 @@ Now let's check its layout fields definition:
 
 [project]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/testdata/project-v3/PROJECT
 [versioning]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/VERSIONING.md#Versioning
-[core-types]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/pkg/plugins/golang/options.go
+[core-types]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/pkg/plugins/golang/options.go
+[deploy-image-plugin]: ../plugins/deploy-image-plugin-v1-alpha.md
+[olm]: https://olm.operatorframework.io/
+[plugins-doc]: ../plugins/creating-plugins.html#why-use-the-kubebuilder-style
+[doc-design-helper]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/designs/helper_to_upgrade_projects_by_rescaffolding.md
+[operator-sdk]: https://sdk.operatorframework.io/